Regardless of the API being confusing or not - using exactly the same
#11125: Typechecker can't infer StM m Bool ~ Bool from StM m a ~ a -------------------------------------+------------------------------------- Reporter: nikomi | Owner: Type: bug | Status: closed Priority: normal | Milestone: Component: Compiler (Type | Version: 7.10.2 checker) | Resolution: invalid | Keywords: Operating System: Unknown/Multiple | Architecture: | Unknown/Multiple Type of failure: None/Unknown | Test Case: Blocked By: | Blocking: Related Tickets: | Differential Rev(s): Wiki Page: | -------------------------------------+------------------------------------- Comment (by nomeata): thing with a vs. any specific type and one works but the other doesn't makes me rather confident something is fishy here :-( `a` can be instantiated to `StM m a` (note that these are different `a`s), but `Bool` cannot be instantiated, and is different from `StM m Bool`. -- Ticket URL: http://ghc.haskell.org/trac/ghc/ticket/11125#comment:7 GHC http://www.haskell.org/ghc/ The Glasgow Haskell Compiler